A conventional heat storage apparatuses is configured such that a heat exchanger is installed in a heat storage tank filled with heat storage medium. In this configuration, circulating water heated by a heat source is delivered to the heat exchanger in the heat storage tank to store heat in the heat storage medium, and cold water supplied through a cold water supply pipe gets heated with the heat extracted from the heat storage medium when it is circulated through the heat exchange, the thus heated water being outputted through a hot water supply pipe (see, for example, Japanese Patent Laid-Open Application No. 2003-232563).
FIG. 10 shows a configuration diagram of the conventional heat storage apparatus disclosed in Japanese Patent Laid-Open Application No. 2003-232563. As shown therein, the conventional heat storage apparatus includes heat storage tank 1, heat storage medium 2, heat exchanger 3, circulating pump 4, heat source 5, hot water supply pipe 6 and cold water supply pipe 7.
However, in accordance with the conventional heat storage apparatus, since the heat is transferred to/from heat storage medium 2 by way of heat exchanger 3, an utilization rate of heat storage medium 2 is reduced, especially in case when a heat pump is employed as a heat source 5, wherein the efficiency is more decreased more noticeably due to an indirect heat exchange of the heat during the heat storage.